The present invention relates to a thermal protector used as means of preventing overheating of electrical equipment accompanied by heat generation such as a fan heater.
FIG. 5 shows a thermal protector disclosed in Japanese Patent Provisional Publication No. 8-222103. In this thermal protector, when electrical equipment such as a fan heater to which the thermal protector is applied generates heat, a bimetal plate 1 performs reversing operation to push up a movable plate 2. Therefore, a movable contact 2 provided at the distal end of the movable plate 2 separates from a fixed contact 3, by which the flow of electric current to the electrical equipment is ceased.
The cease of current flow decreases the heat generation in the electrical equipment. Even when the heat generation temperature becomes lower than the reversing operation temperature of the bimetal plate 1, this electricity shut-off state is maintained. The reason for this is that a heat generating resistor 6 consisting of a thermistor or the like, which is interposed between terminals 4 and 5, generates heat at the same time the contact point 2 separates from the contact point 3, by which the bimetal plate 1 is heated continuously. A function of continuously maintaining the electricity shut-off state (self holding function) is deactivated, for example, by turning off a power switch for the electrical equipment.
For the conventional thermal protector, the heat generating resistor 6 is mounted in such a manner that one and the other electrodes thereof are positioned on the top and bottom faces, respectively. The electrode on the top face side is brought into contact with a plate 7, and the electrode on the bottom face side is brought into contact with the top face of an extension 4a of the terminal 4.
When a construction in which current is carried from the top and bottom faces of the heat generating resistor 6 is used as described above, the size in the thickness direction increases because of the layout of the current-carrying members 7 and 4. Also, construction members must be fixed by tightening rivets 8 and 9, so that much time and labor are required for assembling work.
In order to decrease the size in the thickness direction, the thickness of the resistor 6 may possibly be decreased. In this case, however, the resistor 6 cannot withstand a pressure sufficiently. Also, insulation distances between the plate 7 and the rivet 8 and between the extension of the terminal 4 and the rivet 9 cannot be secured.
There have been proposed a thermal protector in which an electrode plate that is brought into contact with an electrode of a heat generating resistor is provided separately from a terminal, and a thermal protector in which one face of a heat generating resistor is brought into contact with a part of a terminal. Both of these thermal protectors have drawbacks in that the number of parts and the manpower for assembling work increase, resulting in high cost and in that a larger space is required to incorporate the resistor, resulting in increased body shape.
The present invention has been made in view of the above situation, and accordingly an object thereof is to provide a thermal protector capable of incorporating a heat generating resistor without an increase in cost and body shape.
To achieve the above object, the present invention provides a thermal protector comprising first and second terminals connected to external circuits and a heat generating resistor provided with electrodes connected electrically to the first and second terminals on one end face and the other end face thereof, which is constructed so that first and second electrical contacts interposed between the first and second terminals are opened and closed by using the reversing operation of a bimetal plate, wherein a first contact portion is projectingly provided at a part of the first terminal in the direction so as to intersect the bimetal plate, and a second contact portion is projectingly provided at a part of the second terminal so as to be opposed to the first contact portion; and the heat generating resistor is interposed between the first and second contact portions so that the electrodes on one end face and the other end face of the heat generating resistor are brought into contact with the first and second contact portions, respectively.
According to the present invention, since the first and second contact portions serving as current carrying members to the heat generating resistor are provided in the direction so as to intersect the bimetal plate, that is, the contact portions are not in parallel with the bimetal plate, the dimension in the thickness direction can be decreased, so that a compact thermal protector can be realized. That is to say, the dimension in the thickness direction can be made approximately equal to that of a thermal protector of a type having no heat generating resistor. Therefore, the degree of freedom in designing equipment to which the thermal protector is applied increases.
In an embodiment of the present invention, a part of each of the first and second terminals is cut and raised to form first and second support portions, respectively; the proximal end portion of an elastic movable plate provided with the first contact at the distal end thereof is supported by the first support portion, and the second contact opposed to the first contact is supported by the second support portion; and the movable plate is operated by the reversing operation of the bimetal plate so that the first contact is brought into contact with and separated from the second contact.
According to this configuration, the number of additional parts for mounting the heat generating resistor decreases, so that the assembling work can be made easy, and the cost can be decreased.
In an embodiment of the present invention, an elastic element having electric conductivity is interposed between the electrode on one end face of the heat generating resistor and the first contact portion or between the electrode on the other end face of the heat generating resistor and the second contact portion.
According to this configuration, thermal expansion and contraction of each part caused when the thermal protector is used in an environment in which the rise and fall in temperature are repeated are absorbed by the elastic element, so that each of the contact portions can always be brought into contact with the electrode of the heat generating resistor with a proper contact pressure.
In an embodiment of the present invention, an electrical insulating resin block is provided to connect the first and second terminals to each other, and the resin block is provided with a concave for housing the heat generating resistor so that the first and second contact portions are exposed from the opposed inside faces of the concave and the top face of the heat generating resistor is in contact with the bottom face of the concave.
According to this configuration, the heat generated in the heat generating resistor can be dissipated from three faces thereof. Therefore, a larger quantity of heat can be generated by the heat generating resistor.
In an embodiment of the present invention, a groove is formed in the bottom face of the concave in the resin block in the direction along the face of the electrode of the heat generating resistor.
According to this configuration, a space is formed between the bottom face of the concave and the top face of the heat generating resistor, so that the electrical insulation performance between the electrodes of the heat generating resistor can be enhanced when the thermal protector is used in a state of dew condensation.
In an embodiment of the present invention, the elastic element is provided with a holding portion for holding the heat generating resistor in cooperation with the bottom face of the concave in the resin block.
According to this configuration, the heat generating resistor can be held more reliably.